Motor starter



June 23, 1942. B. w JONES 2,287,617

MOTOR STARTER Filed July 3, 1940 Fig I.

l H I \I/ /5 5T0j l8 9 i 5 LETART 2 P05 if Invemtor': Benjamin Wipes, by flan 176 1 W4 Hi S Attorney.

Patented June 23, 1942 MOTOR STARTER Benjamin W. Jones, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application July 3,. 1940, Serial No. 343,791

4 Claims.

This invention relates to starters for electric motors, more particularly to across the line type of starters for A. C. motors, and it has for an object the provision of a simple, reliable, inexpensive, and improved starter of this type.

Another object of the invention is the provision of a starter that can be used in locations in which only A. C. power is available, in which the starting contacts are maintained closed unless the voltage is reduced to a very low value.

Still another object of the invention is the provision of a starter of the character described in which the manual control switch is located in a low voltage control circuit which is insulated from the high line voltage.

A further object of the invention is the provision of a starter of this character in which time delay under-voltage release is provided without the use of dashpots or other time delay devices.

A still further object of the invention is the elimination of all magnetic noises.

In carrying the invention into effect in one form thereof, a magnetic structure is provided which has a channel shape cross section, i. e. it has a floor and two side walls. One side wall comprises a rectangular transformer core member cut away to provide a pair of winding legs. A core piece is secured to the floor member between the two walls, and an armature member is mounted to bridge the space between the free edges of the walls and is pivotally mounted near one of the free edges. A primary transformer winding is mounted on one of the winding legs and a secondary winding is mounted on the other Winding leg. A D. C. coil is mounted on the central core piece. Direct current is supplied to this D. C. coil from a rectifier that is supplied with A. C. voltage from the secondary winding of the transformer in response to the closing of a normally open switching device. Contacts actuated by the armature serve to connect a motor to a source of supply.

For a better and more complete understandin of the invention, reference should now be had to the following specification and to the accompanying drawing in which Fig. 1 is a simple diagrammatical sketch of an embodiment of the invention, and Fig. 2 is an end view of the magnetic structure of the device.

Referring now to the drawing, a magnetic structure ID has a channel shape cross section, i. c. it has a floor member [a and two side wall members Nib and Hie. A core piece H is secured to the floor member We.

An armature member I2 bridges the space between the free edges of the walls lllb, I and thus completes the magnetic circuit of the magnetic structure. The armature is pivotally mounted on a shaft 1'3 near the free edge of the wall Ilia.

The wall Hit of the magnetic structure preferably comprises a plurality of rectangular transformer core laminations cut out to provide a pair of winding legs. The floor member His and side wall Hie are preferably integral with each other so as to form an angle piece which may be joined to the rectangular transformer core in any suitable manner. This angle piece may be made of any suitable magnetic material such as steel.

A primary winding [4 is mounted on one winding leg of the laminated transformer core and this winding is connected to one phase of a source of supply such as the polyphase source represented by the supply lines I5, and a secondary winding I6 is mounted on the other winding leg. These two windings could be mounted on the same winding leg if desired. A D. C. coil I1 is mounted on core piece H. The D. C. coil is connected to the transformer secondary winding It by means of normally open electrical connec tions comprising conductors l8 and I9, normally closed stop push button type switch 20, normally open start push button type switch 2|, and conductors 22 and 23.

A full wave rectifier 24 is included in these connections and supplies direct current to the D. C. coil I! when the start push button switch is closed. This rectifier is mounted in a suitable location on the panel on which the magnetic structure is mounted. Preferably this rectifier is of the surface contact type, such as the well known copper Oxide rectifier. Movable contacts 25 are mounted on shaft I3 and serve to connect induction motor 26 to the source l5. Overload protection is provided by means of overload relays 33 and 34 which have their operating coils connected in the motor leads and their normally closed contacts connected in series relationship with each other in the connections between the transformer secondary winding I6 and rectifier 24.

With the foregoing understanding of the parts and their organization, the operation of the device will be readily understood from the following description:

Switch 2'! is closed to connect the primary ['4 of the transformer to the source. Start push button 2| is then depressed to complete the connections to the rectifier and D. C. coil H. During one-half cycle of the alternating voltage,

current flows from the right-hand terminal of the transformer through conductor 18, stop push button switch 2e, start push button switch in the closed position thereof, arm 24a of rectifier 2 1, conductor 22, D. C. operating coil 11, conductor 23, arm 2% of rectifier 24, and thence through conductor 19 to the left-hand terminal of secondary Winding I5. During the succeeding half-cycle current flows from the left-hand terminal of secondary winding l6 through conductor l9, arm 240 of the rectifier, conductor 22, coil I! in the same direction as in the preceding half-cycle, conductor 23, arm 24d of the rectifier, and thence by switches 2| and 20 and conductor IE to the right-hand terminal of winding it. The magnetic flux set up by coil 11 in core piece H enters the armature l2 and divides, one portion passing through the armature and across the air gap into the side wall I and thence through the floor member Illa to the core piece II, and the other portion taking the opposite path through the armature, across the air gap to the laminated transformer core b, through the core and floor member Ilia to the core piece l I. The turn ratio of the primary and secondary windings of the transformer is such as to produce a low voltage, i. e. 110 or 220 volts in the push button circuit in order to protect the operator against the high voltage of the source which frequently is 440 volts or 550 Volts.

Armature i2 is attracted to its picked up position to close contacts 25 and connect motor 26 to the source i5. Movable interlock member 28 bridges contact members 29 to complete a sealing in circuit for coil ll in parallel with the contacts of start push button 2|, which may now be released.

Ordinarily, an A. C. contactor will drop out at approximately 50% of normal voltage. Although only alternating current is available for the operation of this starter, the rectification of the alternating current and the supply of the rectified current to the coil ll assure that the armature will remain picked up even though the A. C. line voltage decreases to a value as low as 20% of normal line voltage. In other words, the device of this invention has an extremely low voltage release value for an electromagnetic device receiving its excitation from an A. C. source. This low voltage release value can be changed to some extent by adding shims 3B or 3| to the free edges of the core structure.

If the line voltage decreases to zero the armature will remain picked up for a time interval owing to the time constant of the electrical and magnetic circuits of the transformer windings and core, and the D. C. operating winding I1 and core. This time delay will depend to some extent upon the thickness of the shims 30 or 3| in the air gaps between the core and the armature. Consequently, the time delay may be adjusted within limits by choosing shims of the proper thickness.

Since the armature I2 is held picked up against the pole piece 32 of the D. C. core piece H and since the armature does not come in actual contact with the rectangular transformer core structure, the device is free from chattering or other noises which are usually present in electromagnetic devices excited from an A. C.

source.

Although in accordance with the provision of the patent statutes, this invention is described as embodied in concrete form and the principle thereof has been described together with the best mode in which it is now contemplated applying that principle, it will be understood that the invention is not limited to the precise details shown and described, since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of this invention or from the scope of the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A time delay undervoltage release motor starter comprising a magnetic core structure having a floor member and two side walls, one of said side walls being composed of laminations and provided with a primary winding and a secondary winding, means for connecting said primary winding to a source of supply, a core piece secured to said floor member between said side walls, a D. C. operating coil mounted on said core piece, electrical connections between said secondary winding and said D. C. coil, a rectifier included in said connections for supplying direct current to said operating coil thereby to provide quiet operation, a switching device included in said connections, an armature member pivotally mounted near the free edge of one of said walls and arranged to bridge the space between the free edges of aid walls when attracted to its picked up position in response to energization of said operating coil and contacts actuated by movement of said armature for connecting a motor to a source of supply.

2, A motor starter comprising a magnetic core structure having a floor member and two side walls, one of said walls having a window providing two winding legs, a transformer primary winding mounted on one of said legs and provided with connections to an alternating current source, a secondary winding on the other of said legs, a core piece secured to said floor member between said side walls, a D. C. coil on said core piece, electrical connections between said secondary winding and said D. C. coil, a control switching device and a rectifier included in said connections whereby direct current is supplied to said D. C. coil when said switching device is closed, an armature member pivotally mounted near the free edge of one of said walls and arranged to bridge the space between the free edges of said walls when attracted to its picked up position in response to energization of said D. C. coil and contacts actuated by movement of said armature for connecting a motor to a source of supply.

3. A motor starter comprising a magnetic core structure having a floor member and two side walls, one of said side walls being cut away to provide a rectangular transformer core member having two winding legs, an armature member arranged to bridge the space between the free edges of said walls, a core piece mounted on said floor member between said walls, a primary transformer winding on one of said legs and hav ing connections to a source of alternating voltage, a secondary winding on the other of said legs, a D. C. coil mounted on said core piece, normally open electrical connections between said secondary winding and said D. C. coil, a rectifier included in said connections between said secondary winding and said D. C. coil, a switching device having normally open contacts included in said connections for causing direct current to be supplied to said coil in response to the closing of said contacts thereby to attract said armature to the picked up position and contacts actuated by said armature for connecting a motor to a source of supply.

4. An across the line type motor starter comprising a magnetic core structure having a floor member and two side walls, one of said walls comprising a laminated rectangular transformer core member cut out to provide a plurality of winding legs, an armature arranged to bridge space between the free edges of said walls and pivotally mounted near one of said edges, a core piece secured to said floor member between said wall members, a surface contact rectifier, a trans former primary winding mounted on one of said winding legs provided with connections to an A. C. source, a secondary winding mounted on the other of said Winding legs, a D. C. coil mounted on said core piece, normally open electrical connections from said secondary winding to said coil, said rectifier being included in said connections, a master control switch for closing said normally open connections to cause direct current to be supplied to said coil thereby to attract said armature to its picked up position, contacts actuated by said armature for connecting a motor to a source of supply, and an interlock actuated by said armature for maintaining said rectifier connected to said secondary Winding when said master control switch is opened.

BENJAMIN W. JONES. 

